I use xDrip+ on my Android phone and document all the carbs/insulin/comments. It has an IOB calculator which works well for me when the basal is set ok.
I have to say that xDrip+ with my pebble watch has been a gamechanger for me and I keep on top of things much better that 3 months ago. It is only getting better.
Today is not a flatline day - someone didn't adequately prebolus for something he consumed at a social event but I post to show the IOB feature. It really helps me a lot.
EDIT - actually looking at it another way, it was a good catch on a bad morning carb count with a correction bolus and then a prebolus for lunch with a post prandial landing near target and no post meal spike